Everything you bring with you you will have to carry on your bike. Keep this in mind when packing! To pack for your bicycle trip along the Canal Du Midi you should carefully read the next few paragraphs.
You want to focus on clothing that is lightweight and multi-purpose. Also keep in mind the weather in the area during the time of year you plan to cycle. With this said, it thus should make sense to NOT bring your leather jacket (not lightweight or multi-purpose), NOT bring your dancing shoes or high heels (again, not multi-purpose), and NOT bring your ski jacket in July (wrong time of year).
You should aim for clothes that can be layered. A loose fitting long sleeve shirt, a long sleeve button down shirt, and a high visibility waterproof/breathable shell layer make for an excellent combination. A wool sweater or fleece jacket will protect you from the cooler nights.
Other essentials include a helmet and cycling gloves. The path along the Canal Du Midi is bumpy, thus a helmet and gloves are recommended.
Bicycle shoes, bicycle shorts, bicycle jerseys are not essential.
Try keeping the total weight in your panniers below 20 Kilograms. Heavy items should be placed into your front panniers, while large bulky items should be placed in your rear panniers for best bicycle performance. Some people claim 60 percent of the total weight should be placed into the front panniers, and 40 percent in the rear panniers, but this varies between riders.
It is a good practice to put your items into transparent plastic bags. This will help in several ways. Firstly, some panniers labeled water-proof can still leak in a heavy downpour or if used improperly (over filled for example). The plastic bags act like an insurance policy for your items, you most likely will not need them but they are good to have just in case. Secondly, having your items in separate bags will make it much easier to find something quickly, as you can simply pull out 2 or 3 bags to get to the last bag at the very bottom of your pannier to get a new pair of socks for example. Keep a few empty plastic bags on hand to fill with dirty clothes. It is easiest to roll your clothing instead of folding them.
Try to keep the total weight of the load on the trailer below 20 Kilograms. The heaviest items should be placed as close to the ground as possible, thus keeping the trailers center of gravity low. This will increase the trailer's stability. Just as packing your panniers, the use of transparent plastic bags to sort your items is recommended.
Small items that you want to keep in easy reach should be placed in the handlebar bag. Most handlebar bags can be detached to that they can serve as a shoulder bag (make sure you do not forget your shoulder strap at home). The handlebar bag is the best place for your camera, wallet, phone. These small items should not be put into your pant pockets, as they are prone to fall out on a bumpy track like the Canal Du Midi towpaths. If a handlebar bag is not available, a small backpack or fanny pack will suffice as well. Limit your weight to about 3 Kilograms for the handlebar bag.
Once you have sorted your luggage, it is time to do a dry run. Pack your panniers and take your bike for a ride. Still need that third pair of pants? Still need that "Definite encyclopedia of cake baking" book? Now is your chance to take them out and leave them at home. You can always buy another pair of pants if really needed, or download your favorite book onto your phone or ipad instead.
Making an exact list of items to bring is next to impossible. The items below are just a suggestion. It is said that the number of items needed for a one week tour is equal to the number of items needed for a three month tour.